Studies on the regulation of the yeast glutamate dehydrogenases (GDH) were continued. Both the active (dephospho-) NADH-GDH and the less active (phospho-) NAD-GDH have been purified to homogeneity and characterized. Two cyclic nucleotide independent protein kinases have been partially purified and shown to be capable of phosphorylating NAD-GDH. Phosphorylation of NAD-GDH in vitro does not result in enzyme inactivation. The role of yeast protease in the regulation of NADP-GDH, during carbon starvation, was investigated using mutant strains of Saccharomyces cerevisiae deficient in certain protease activities. Strains lacking protease B activity or with low levels of protease A, B, and carboxypeptidase Y inactivated (degraded) NADP-GDH at a similar rate to that observed with the wild type parent strain. The processing of procarboxypeptidase Y was investigated in protease deficient yeasts. One of the mutants was found to synthesize procarboxypeptidase, but did not process (activate) the enzyme thus lacking any carboxypeptidase activity.